Mac OS X: ScreenSharingMenulet gives you easy access to local, remote and Back to My Mac VNC servers directly from your OS X menubar. It's customisable, lightweight and completely necessary if you make heavy use of VNC.
I've used ScreenSharingMenulet for a long time and how it's taken so long to write it up is just shameful. It's one of the most useful utilities for when you have multiple Macs and one of the first things I install on a new machine. It's pretty simple in its functionality, but it allows for a fair amount of customisation. It'll pull any screen-sharing options you'll see in the Finder, but if you have a specific IP address you want to add you can manage those easily in preferences.
ScreenSharingMenulet doesn't do much, but what it does is incredibly useful. It's completely free and available right now (as it has been for a long time before this unfortunately late mention).